The reliable supply of electricity is important for businesses and homes. Indeed, virtually every business and home relies upon the continuous supply of electricity to refrigerate food, to operate heating and cooling systems and many other appliances.
In some applications, the uninterrupted supply of electricity is absolutely critical. For example, computer systems generally require a virtually perfect power supply. Even a momentary glitch can disrupt their operation. Consequently, where the supply of electricity is unreliable, back-up power sources commonly referred to uninterrupted power supplies are used. These usually include a power detection and filtering circuit. If the main power fails, the back-up power source immediately detects the failure and switches to a battery or other back-up source. In more sophisticated systems, the back-up power source will switch to an alternative power supply such as a generator if the main power remains off line.
Although these types of systems are effective even for the most demanding of applications, they are also expensive. The circuitry required to monitor the main power supply and associated battery back up are relatively complex. Moreover, this type of uninterrupted power supply is not necessary for many applications. For example, many businesses or homes can tolerate a short interruption in their power supply. Interruptions of only a few minutes have little effect on heating or cooling systems. Critical applications such as a computer can depend upon a local back-up power supply. If the main power supply continues to fail, a local generator can be started to provide back-up power.
The installation of a back-up generator requires that it is connected into the loading circuits in a manner that does not interfere with the normal delivery of power from a local utility company. The back-up generator must be disconnected when the local utility company provides power to prevent large flows of electricity between the two sources. In most conventional home or business settings, the internal wiring is connected directly to the local utility company through a power meter and breaker switches. The power meter is used to monitor usage for billing purposes. The breaker switches are used to prevent excessive flow of current through any loading circuit.
The addition of an auxiliary power supply requires a switch which is capable of handling the current drawn by an entire home or business. Especially in larger business applications, the total current drawn from a back-up power supply or from the power grid can be substantial. The switch must be able to handle large currents without heating. In order to do so, electrical transfer switches are typically very large. In order to avoid heating at the switch contacts, these are very substantial in size. A transfer switch suitable for high-current applications which is relatively small is desired.